Device with light-emitting diode circuits
Devices (1) have branches (20,30) for receiving AC voltages. First branches (20) comprise first light-emitting diode circuits (21) and first arrangements for phase-shifting first currents flowing through the first light-emitting diode circuits (21) with respect to the AC voltages. Second branches (30) comprise second light-emitting diode circuits (31) and do not comprise second arrangements for phase-shifting second currents flowing through the second light-emitting diode circuits (31) with respect to the AC voltages. As a result, an overall flicker index of the device (1) will be smaller than individual flicker indices of the light-emitting diode circuits (21,31). The first arrangements may comprise capacitors (22) coupled serially to the first light-emitting diode circuits (21). The branches (20,30) may further comprise resistors (23,33) coupled serially to or forming part of the light-emitting diode circuits (21,31). The light-emitting diode circuits (21,31) generate light in response to positive and negative halves of the AC voltages.
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The invention relates to a device comprising light-emitting diode circuits, and to a method for feeding light-emitting diode circuits in a device.
Examples of such a device are lamps comprising alternating current light-emitting diodes or ACLEDs.
BACKGROUND OF THE INVENTIONWO 2005/120134 discloses a circuit comprising two anti-parallel connected light-emitting diodes in a first branch and two anti-parallel connected light-emitting diodes in a second branch. The first and second branches are parallel branches. The first branch further comprises a capacitor and is a capacitive branch. The second branch further comprises a coil and is an inductive branch. As a result, light changes of the anti-parallel light-emitting diode pairs take place at different points in time and, as compared to individual flicker indices of the anti-parallel light-emitting diode pairs, an overall flicker index of the circuit is reduced.
OBJECT AND SUMMARY OF THE INVENTIONIt is an object of the invention to provide an improved device. It is a further object of the invention to provide an improved method.
According to a first aspect of the invention, a device comprises light-emitting diode circuits with at least first and second branches for receiving an AC voltage, wherein the first branch comprises a first light-emitting diode circuit as well as a first arrangement for phase-shifting a first current flowing through the first light-emitting diode circuit with respect to the AC voltage, and the second branch comprises a second light-emitting diode circuit and does not comprise a second arrangement for phase-shifting a second current flowing through the second light-emitting diode circuit with respect to the AC voltage.
A simple and low-cost, robust device is created by phase-shifting a first current flowing through the first light-emitting diode circuit with respect to the AC voltage, and by not phase-shifting a second current flowing through the second light-emitting diode circuit with respect to the AC voltage.
A light-emitting diode circuit comprises one or more light-emitting diodes, (in)organic light-emitting diodes and/or laser light-emitting diodes.
The first and second branches may be parallel branches and/or branches powered from the same secondary winding or from different secondary windings of a transformer. Each branch may further comprise one or more other components such as a relay, a switch, a fuse, etc.
In an embodiment of the device according to the invention, the first arrangement comprises a capacitor coupled serially to the first light-emitting diode circuit. Use of a capacitor for phase-shifting a current is advantageous as compared to using a coil, because the capacitor has a smaller size. In addition, the first arrangement may further comprise one or more other capacitors and/or one or more resistors.
In another embodiment of the device according to the invention, the capacitor is controllable. Said controllability may comprise, for example, changing the physical properties, such as size, distance, etc. of the capacitor and/or may have a dedicated control input and/or several capacitors of different size and selection means, e.g. a second capacitor, which can be connected in parallel or in series with the first capacitor by means of one or more controllable switches, and/or may comprise applying a control voltage across the capacitor by means of a suitable decoupling network so as to advantageously adjust the capacitive current phase angles, e.g. to optimize the power factor of complete lamp systems. The controllability of the capacitor can be utilized e.g. during production of the devices (e.g. laser trimming of the capacitor size), during production of luminaries consisting of one or more devices, or during operation so as to achieve a desired operating point.
In a further embodiment of the device according to the invention, the respective first and second branches further comprise respective first and second resistors coupled serially to or forming part of the respective first and second light-emitting diode circuits. The respective first and second resistors may be located either outside or inside the respective first and second light-emitting diode circuits. When located outside the respective first and second light-emitting diode circuits, the first resistor may be located between the capacitor and the first light-emitting diode circuit, or the capacitor may be located between the first resistor and the first light-emitting diode circuit, or the first light-emitting diode circuit may be located between the capacitor and the first resistor. When located inside the respective first and second light-emitting diode circuits, the resistors may be external or internal resistors realized by properly selecting and/or coupling the light-emitting diodes. In addition, each branch may further comprise one or more other resistors.
In a further embodiment of the device according to the invention, one or more of the first and second resistors is controllable. Said controllability may comprise, for example, changing the physical properties, such as length, width, etc. of the resistor and/or may have a dedicated control input and/or several resistors of different size and selection means, e.g. a third resistor, which can be connected in parallel or in series with the first or second resistor by means of controllable switch(es), and/or may comprise applying a control voltage across the resistor by means of a suitable decoupling network so as to advantageously adjust the capacitive current phase angles, e.g. to optimize the power factor of complete lamp systems. The controllability of the resistor can be utilized e.g. during production of the devices (e.g. laser trimming of the resistor width), during production of luminaries consisting of one or more devices or during operation so as to achieve a desired operating point.
In a further embodiment of the device according to the invention, one or more of the first and second light-emitting diode circuits is controllable. Said controllability may comprise, for example, adjusting the wiring of the light-emitting diode circuit by means of laser trimming, etc.
In a further embodiment of the device according to the invention, at least one of the light-emitting diode circuits is capable of generating light in response to at least a part of a positive half of the AC voltage as well as in response to at least a part of a negative half of the AC voltage. Such a light-emitting diode circuit is preferably to be used when being fed with an AC voltage.
In a further embodiment of the device according to the invention, at least one of the light-emitting diode circuits has substantially similar impedance values for both halves of the AC voltage. Such a light-emitting diode circuit is preferably to be used when an overall flicker index of the device is to be reduced as compared with individual flicker indices of the light-emitting diode circuits. The flicker index is related to, for example, the optical flicker index in the emitted light in accordance with the IESNA calculation method.
In a further embodiment of the device according to the invention, at least one of the light-emitting diode circuits comprises two anti-parallel strings each consisting of one or more light-emitting diodes.
In a further embodiment of the device according to the invention, at least one of the light-emitting diode circuits comprises a rectifier coupled serially to a string of one or more light-emitting diodes.
In a further embodiment, the device is an AC voltage lamp comprising a light source, the first and second light-emitting diode circuits jointly constituting the light source.
In a further embodiment of the device according to the invention, the respective first and second light-emitting diode circuits generate light with respective first and second flicker indices, and the light source generates light with an overall flicker index which is smaller than each one of the first and second flicker indices.
In a further embodiment of the device according to the invention, a sum of the first and second currents is a total current, the total current having a reduced third harmonic as compared to each one of the first and second currents. A reduction of the third harmonic of the total current supplied by an AC voltage source is a great advantage in striving for compliance with mains harmonics regulations.
In a further embodiment of the device according to the invention, each phase-shifting corresponds to an introduction of a phase shift of at least five degrees. In the first branch, the first current flowing through the first light-emitting diode circuit is thus shifted by at least five degrees (preferably more than five degrees, such as twenty degrees or more) with respect to the AC voltage, and in the second branch, the second current flowing through the second light-emitting diode circuit is shifted by at most five degrees (preferably less than five degrees, such as one degree or less) with respect to the AC voltage.
According to a second aspect of the invention, a method of feeding light-emitting diode circuits in a device with at least first and second branches for receiving an AC voltage is provided, wherein the first branch comprises a first light-emitting diode circuit, and the second branch comprises a second light-emitting diode circuit, the method comprising the steps of phase-shifting , in the first branch, a first current flowing through the first light-emitting diode circuit with respect to the AC voltage, and not phase-shifting, in the second branch, a second current flowing through the second light-emitting diode circuit with respect to the AC voltage.
Embodiments of the method correspond to the embodiments of the device.
The invention is based on the recognition that currents in different branches need to have different phase shifts and that, in only one of two branches, a current needs to be phase-shifted with respect to an AC voltage.
The invention provides an improved device which is simple, low cost and robust.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
In the drawings:
One or more pieces of the device 1 may be monolithically integrated on one or more pieces of semi-conductive material or another type of material, different numbers of junctions may be present in one package or in different packages, and many other different embodiments and implementations are not to be excluded. One or more pieces of the device 1 may be integrated with one or more other pieces of the device 1. One or more pieces of the device 1 may comprise one or more parasitic elements and/or may be based on a presence of these one or more parasitic elements. The AC voltage may be 110 Volt, 220 Volt, 12 Volt or any other type of AC voltage.
The actual waveform and hence the flux of a light-emitting diode circuit is determined by a selection of the light-emitting diode circuit, a selection of a voltage frequency of a waveform of the AC voltage and/or a selection of a capacitor and/or a resistor coupled to this light-emitting diode circuit. These selections determine the harmonics generated by the device and all of this therefore has to be taken into account when designing a device that has to be in compliance with mains harmonics regulations.
In a device, an arrangement may be adjustable to a desired phase-shifting degree, a capacitor may be adjustable to a desired capacitance value, a resistor may be adjustable to a desired resistance value, and a light-emitting diode circuit may be adjustable to a desired light-emitting diode circuitry value. In a method, a step may comprise an adjustment of a controllable element (an arrangement, a capacitor, a resistor, a light-emitting diode circuit) of the device in order to achieve a desired operating point, during production/assembly and/or during operation.
In summary, devices 1 have branches 20,30 for receiving AC voltages. First branches 20 comprise first light-emitting diode circuits 21 and first arrangements for phase-shifting first currents flowing through the first light-emitting diode circuits 21 with respect to the AC voltages. Second branches 30 comprise second light-emitting diode circuits 31 and do not comprise second arrangements for phase-shifting second currents flowing through the second light-emitting diode circuits 31 with respect to the AC voltages. As a result, an overall flicker index of the device 1 will be smaller than individual flicker indices of the light-emitting diode circuits 21,31. The first arrangements may comprise capacitors 22 coupled serially to the first light-emitting diode circuits 21. The branches 20,30 may further comprise resistors 23,33 coupled serially to or forming part of the light-emitting diode circuits 21,31. The light-emitting diode circuits 21,31 generate light in response to positive and negative halves of the AC voltages.
While the invention has been illustrated and described in detail in the drawings and the foregoing description, such an illustration and description are to be considered illustrative or as examples, and are not restrictive; the invention is not limited to the disclosed embodiments. For example, it is possible to operate the invention in an embodiment wherein different parts of the different disclosed embodiments are combined to a new embodiment.
Other variations of the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, use of the verb “comprise” and its conjugations does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.
Claims
1. A device comprising light-emitting diode circuits with at least first and second branches for receiving an AC voltage, wherein the first branch (20) comprises a first light-emitting diode circuit and a first arrangement for phase-shifting a first current flowing through the first light-emitting diode circuit with respect to the AC voltage, and the second branch comprises a second light-emitting diode circuit and does not comprise a second arrangement for phase-shifting a second current flowing through the second light-emitting diode circuit with respect to the AC voltage.
2. The device as claimed in claim 1, wherein the first arrangement comprises a capacitor coupled serially to the first light-emitting diode circuit.
3. The device as claimed in claim 2, wherein the capacitor is controllable.
4. The device as claimed in claim 2, wherein the first and second branches (20,30) further comprise respective first and second resistors (23,33) coupled serially to or forming part of the respective first and second light-emitting diode circuits.
5. The device as claimed in claim 4, wherein the first and second resistors (23,33) are controllable.
6. The device as claimed in claim 1, wherein the first and second light-emitting diode circuits are controllable.
7. The device as claimed in claim 1, wherein at least one of the light-emitting diode circuits is capable of generating light in response to at least a part of a positive half of the AC voltage as well as in response to at least a part of a negative half of the AC voltage.
8. The device as claimed in claim 1, wherein at least one of the light-emitting diode circuits has substantially similar impedance values for both halves of the AC voltage.
9. The device as claimed in claim 1, wherein at least one of the light-emitting diode circuits comprises two anti-parallel strings each comprising one or more light-emitting diodes.
10. The device as claimed in claim 1, wherein at least one of the light-emitting diode circuits comprises a rectifier coupled serially to a string of one or more light-emitting diodes.
11. The device as claimed in claim 1, wherein the device is an AC voltage lamp comprising a light source, the first and second light-emitting diode circuits jointly constituting said light source.
12. The device as claimed in claim 11, wherein the first and second light-emitting diode circuits generate light with respective first and second flicker indices, and the light source generates light with an overall flicker index which is smaller than each one of the first and second flicker indices.
13. The device as claimed in claim 1, wherein a sum of the first and second currents is a total current, the total current having a reduced third harmonic as compared to each one of the first and second currents.
14. The device as claimed in claim 1, wherein each phase-shifting corresponds to an introduction of a phase shift of at least five degrees.
15. A method comprising providing a device, wherein the device has at least first and second branches (20,30) for receiving an AC voltage, wherein the first branch (20) comprises a first light-emitting diode circuit, and the second branch comprises a second light-emitting diode circuit, the method further comprising the steps of phase-shifting, in the first branch (20), a first current flowing through the first light-emitting diode circuit with respect to the AC voltage, and not phase-shifting, in the second branch, a second current flowing through the second light-emitting diode circuit with respect to the AC voltage.
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Type: Grant
Filed: Jul 22, 2009
Date of Patent: Jun 18, 2013
Patent Publication Number: 20110115389
Assignee: Koninklijke Philips N.V. (Eindhoven)
Inventor: Harald Josef Gunther Radermacher (Aachen)
Primary Examiner: Thuy Vinh Tran
Application Number: 13/055,517
International Classification: H05B 37/02 (20060101);